1. Field of the Invention
The present invention relates to a metallic gasket material that provides a base for making a cylinder head gasket adapted for use on the cylinder head of an internal-combustion engine or like gasoline engine mounted on an automotive vehicle, and more particularly to such a cylinder head gasket that comprises a thin spring steel sheet having beads formed thereon.
2. Description of the Prior Art
Typically, a conventional metal cylinder head gasket includes an elastic metal sheet having beads formed like projections or steps in cross section, wherein the said beads may serve to seal the joint surfaces between the cylinder head and cylinder block of an internal-combustion engine, for example. This gasket provides an effective means for sealing the joint, and has been employed for the practical use in the fields, such as the automobile engines. In general, the cylinder head gasket has a coating of an elastic sealing material containing a rubber material as a base component applied on the front side or rear side, or both, of the cylinder head gasket, as disclosed in Japanese patent application now laid open to public inspection under Japanese Patent Publication No. 63-A-96359. The coating of an elastic sealing material is provided to increase the sealing capability of the gasket.
For recent years, there have been demands for small-size, light-weight engines as well as for engines that produce less exhaust gases. For the small-size, light-weight engines, the engines might lose the mechanical rigidity by themselves, whereas for the less exhaust gas engines, the engines might produce higher temperatures. Thus, demands arise for cylinder head gaskets that address the above problems and solve them effectively.
For the engines that has the rigidity problem as firstly mentioned, using the conventional cylinder head gasket to close the cylinder block of the engine tightly would tend to cause the deformation on the cylinder block by the tightening action. This would make it difficult to apply the uniform tightening force to the cylinder head gasket to tighten the cylinder block.
For the engines that has the high temperature problem as secondly mentioned, there is a remarkable difference in the temperature between the exhaust port side and suction port side of the cylinder block, which would cause the thermal deformation to develop on the joint between the cylinder head and cylinder block. When the conventional cylinder head gasket is used on such engines, the part of the gasket that seals the joint between the cylinder head and cylinder block would develop a partial difference in the surface pressure upon the joint. If any excessive temperature differential should occur, the coating of the elastic sealing material including a rubber base on the cylinder head gasket would be degraded by the thermal effect, which would subject the coating of the sealing material to the stress relief. Thus, the restorability of the gasket required to seal the joint would be reduced considerably.
One possible solution to the above problem is to use the elastic sealing material that contains any rubber material that has the good thermal resistance, and to employ such elastic sealing material for the gasket. But, this would have the unfavorable effect of increasing the manufacturing cost and therefore the product cost, which is not desirable for the practical and commercial reasons.
The present invention addresses the problems of the conventional cylinder head gasket as described above, and provides a cylinder head gasket that solves both the rigidity problem of the engine itself and the high temperature problem of the engine in an effective manner.
Specifically, it is an object of the present invention to provide a cylinder head gasket when it is used to close the cylinder block of the engine, the uniform tightening force can be applied to the cylinder block and cylinder head by the said cylinder head gasket, while the said cylinder head gasket can provide the constant surface pressure even when it is exposed to the excessive temperature differential caused by the rising temperature within the engine, and can maintain the restorability and conformability of the gasket that are required to seal the cylinder head for a long time under such situations.
More specifically, the present invention proposes to provide a cylinder head gasket for an internal-combustion engine that comprises an elastic metal sheet having more than one combustion chamber openings or orifice and more than one passage hole, wherein the elastic metal sheet has a bead formed in the area surrounding the combustion chamber opening and a bead formed in the area surrounding the passage hole, respectively, and has a coating of a sealing material on the front side or rear side, or both, of the elastic metal sheet.
In order to overcome the problems described above, the cylinder head gasket according to the present invention has the following features that characterize the present invention, which will be described below.
One of the features is that the sealing material that may be used to form a coating layer on the front side or rear side, or both, of the bead formed in the area surrounding the combustion chamber openings includes any thermally resistant sealing material. Another feature is that the sealing material that may be used to form a coating layer on the bead formed in the area surrounding the passage holes includes any water/oil resistant sealing material.
In other words, the area surrounding the combustion chamber opening that is exposed to the high temperatures has a coating of the sealing material that can meet the requirements for the high temperature resistance, and the area surrounding the passage hole that is required to provide the high sealing capability against the water and/or oil have a coating of the sealing material that can meet the requirements for the water/oil resistance.
In the cylinder head gasket according to the present invention, the thermally resistant sealing material may be composed of a principal component of fluorine rubber, and any one or ones of the components consisting of expanded graphite, organic fiber, inorganic fiber, organic filler, inorganic filler, and synthetic resins.
The fluorine rubber is highly resistant to the heat, but is expensive. Thus, using lots of fluorine rubber would increase the manufacturing cost, which increases the product cost accordingly. In the cylinder head gasket according to the present invention, however, it may be appreciated from the foregoing description that the coating of the thermally resistant sealing material may only be applied to the bead formed in the area surrounding the combustion chamber openings that are exposed to the high temperatures in the combustion chamber, and that the said thermally resistant sealing material may be composed of the principal component of the fluorine rubber, and any one or ones of the components mentioned above. This can tend to maintain the highly thermal resistance of the sealing material while reducing the manufacturing cost.
In the cylinder head gasket of the present invention, the sealing material that provides the water and/or oil resistance may be composed of a rubber material, and any inorganic fiber or organic fiber.
In the cylinder head gasket of the present invention, the bead formed in the area surrounding the combustion chamber opening may preferably be formed like a full bead having the convex shape in cross section that can provide the spring action, since the area surrounding the combustion chamber opening is always exposed to the high temperatures and high pressures that are developed within the combustion chamber.
Similarly, the bead formed in the area surrounding the passage hole may preferably be formed like a half bead having the stepped shape in cross section that can provide the surface pressure adjusting function.
In the cylinder head gasket of the present invention, the bead formed in the area surrounding the combustion chamber opening may have a coating of the thermally resistant sealing material applied on both of the front and rear sides thereof. In this case, it is preferable to differ at least any one of parameters of the thermally resistant sealing material applied on the front side, such as the types of components, the composition ratio of components, the hardness, and the thickness of the thermally resistant sealing material applied on the front side, to that of the thermally resistant sealing material applied on the rear side.
This may also apply when the bead formed in the area surrounding the passage hole has a coating of the water/oil resistant sealing material applied on both of the front and rear sides thereof. At least any one of the parameters, such as the types of components, the composition ratio of components, the hardness, and the thickness of the water/oil resistant sealing material applied on the front side may be different from that of the water/oil resistant sealing material applied on the rear side.
Thus, the parameters such as the hardness and thickness of the coating of the sealing material to be applied, and the types and composition ratios of the components may be chosen differently for each of the front and rear sides, and the combination of the parameters chosen may be varied, depending on the respective requirements for each of the front and rear sides. In this way, according to the present invention, different cylinder head gaskets can be made in order to meet their respective different requirements.
It should be noted that the cylinder head gasket of the present invention may have a multiple construction that includes several cylinder head gaskets that are placed one over another like a stack, and may be mounted as a single unit on the engine such as the internal combustion engine.
According to the cylinder head gasket of the present invention, it may be appreciated that the coating of the sealing material that is applied on the bead formed in the area surrounding the combustion chamber opening that is exposed to the high temperatures and high pressures within the combustion chamber may have the appropriate properties to meet the particular requirements, and the coating of the sealing material that is applied on the bead formed in the area surrounding the passage hole that is required to provide the high sealing capability against the water and/or oil may also have the appropriate properties to meet the particular requirements. Furthermore, the bead formed in the area surrounding the combustion chamber opening and the bead formed in the area surrounding the passage holes may be formed into the appropriate shape to meet the particular requirements, respectively. The cylinder head gasket of the present invention that incorporates the features described above can solve the rigidity problem of the engine itself as well as the high temperature problem of the engine, and can be obtained at a reduced manufacturing cost.
More specifically, even if the cylinder block of the engine has been deformed, and the cylinder head gasket of the present invention is used to tighten the said deformed cylinder block, the uniform tightening force can be applied to the cylinder block and the cylinder head by the cylinder head gasket.
Even if the cylinder head gasket of the present invention is exposed to any excessive temperature differential that may be caused by the rising temperature within the combustion chamber, the part of the cylinder head gasket that seals the cylinder block can continue to exert the constant surface pressure upon the cylinder block. As the sealing material contains a rubber material having the appropriate properties to meet the respective requirements for the area of the elastic metal sheet on which the coating of such sealing material is applied, respectively, the cylinder head gasket thus obtained can provide the long-lasting restorability and conformability that are required to seal the cylinder block.
Although the sealing material used in the cylinder head gasket of the present invention contains the expensive fluorine rubber as the thermally resistant component, and is used to apply the coating to the elastic metal sheet, the coating of such sealing material may be limited to those regions that require the thermal resistance. Thus, the cylinder head gasket can he manufactured at the reduced costs and with the reduced size and weight.